The trucking industry is an essential element in our interstate commerce system. Shipment of goods by tractor-trailer rig is an inexpensive way to distribute goods throughout the country. One drawback to this system is that these large and heavy vehicles share the open highways with the motoring public. Therefore, it is essential that tractor-trailer rigs be operated in a safe manner and have the best safety equipment available.
Many tractor-trailer rig drivers, particularly independent tractor-trailer operators, drive one particular tractor all the time. The trailers that they tow are normally owned, operated and maintained by separate entities. The independent tractor-trailer operator is hired to transport trailers from one location to another. The operator traverses the country, hauling one or more trailers from one location to the next, picking up a different trailer or trailers, and then moving on. Thus, more than one entity is responsible for the maintenance and safety equipment of a tractor-trailer rig on the highway. More important, the operator is intimately familiar with the characteristics and equipment of the tractor he drives, but not of the trailer he pulls with that tractor.
Quite possibly, the most important piece of safety equipment on a tractor-trailer rig is the brake system. In an emergency, the operator depends on the brake system to stop a tractor-trailer rig that can weigh 50,000 pounds or more. The brakes located on the tractor and on the trailers must work together to slow down a tractor-trailer rig.
An important device in any tractor-trailer brake system is the gladhand. A gladhand is the coupling between the tractor and trailer air brake lines. The gladhand communicates between the brakes located on the tractor and the brakes located on the trailer.
When the truck driver pushes down on the brake pedal in the tractor, the air pressure in the tractor brake line is increased rapidly to apply the brakes on the tractor. This air pressure is simultaneously transferred through the gladhand to apply the brakes on the trailer. When the operator releases the brake pedal, the brake system at the tractor has its own exhaust system to release air pressure. In the past, this exhaust has also provided the pressure release for the trailer brakes. However, the response time for the trailer brakes after the brake pedal was released was undesirably long. For some long rigs, the release time may be from one to one and one-half seconds.
This time delay causes serious safety concerns. Inexperienced drivers may accelerate before the brakes fully release. In other situations, the tractor-trailer rig will roll after the brake pedal is released. Both situations cause unnecessary wear to brake drums, shoes and tires. In a situation where the road surface is slick or icy, skidding or sliding is a hazard and can cause serious accidents.
A recent improvement in the standard gladhand has been the addition of a quick-release valve at the gladhand apparatus. The quick-release valve shortens the brake release time at the trailer. Thus, the overall safety of the tractor-trailer is enhanced.
The integration of a quick-release valve and a gladhand device is taught by Jacobs et al., U.S. Pat. No. 4,733,919 and by Berg and Skurka, Canadian Patent No. 1,225,904. Both references disclose gladhand devices with quick-release valves mounted on the trailer, as opposed to the tractor. Jacobs states that optimum results are obtained when the gladhand and quick-release valve is mounted at the forward end of the trailer and states that it is desirable to provide such a device at the forward end of the trailer. See, Jacobs Col. 2, lines 24-33; Col. 3, lines 53-55. The Berg reference also teaches a combination gladhand and quick-release valve mounted at the trailer or between two trailers.
A disadvantage of the teachings of Jacobs and Berg is the suggestion that the gladhand and quick-release valve is desirably mounted on the trailer, as opposed to the tractor, of a tractor-trailer rig. The driver is not assured that a particular trailer he is pulling at the moment is equipped with an integrated gladhand and quick-release valve. Even if the driver hooked up the gladhand, he may respond incorrectly in an emergency or forget whether the trailer he is currently pulling has a quick release valve.
Another phenomenon that contributes to the slow response of the trailer brakes to the release of the brake pedal is hysteresis. Hysteresis is a retardation or a lagging of the effect when the forces acting upon a body are changed. In the case of a tractor-trailer brake system, hysteresis refers to the slow response time of the tractor-trailer brakes when the operator releases the brake pedal. This hysteresis is caused by a pressure difference between the input and output lines of a combined gladhand and quick release valve before the brakes are applied or released.